PROBLEM TO BE SOLVED: To aim at the improvement of measurement accuracy and to improve the brightness of an image that expresses oxygen saturation about the oxygen saturation concerning a surface blood vessel and an intercellular layer blood vessel without causing an increase in production cost and the complication of device configuration in an endoscope system.SOLUTION: A light source device of the endoscope system has a white light source. On an optical path of the white light source, a rotary filter that separates white light into three colors of B, G and R, and a band pass filter that color-separates narrow band light N from white light are freely insertably and removably arranged. The band pass filter is to generate oxidimetry light to measure the oxygen saturation of blood hemoglobin, and has an optical characteristic that penetrates two narrow band lights N11 and N12 of a wavelength band region in which the magnitude correlation of the absorption constant of oxygenated hemoglobin and reduced hemoglobin is same. The measurement accuracy and the brightness of the image are improved because the oxidimetry light becomes a quantity of light that matches the two narrow band lights N11 and N12.
